Field of the Invention
The present invention relates to a multistage transmission device employed in a vehicle such as a motorcycle.
Description of the Related Art
An engine mounted in a vehicle such as a motorcycle is equipped with a multistage transmission device. The multistage transmission device has a countershaft that receives a drive force from a crankshaft through a clutch mechanism and a drive shaft that outputs the drive force received from the countershaft. A plurality of gears having different numbers of teeth is provided in both the shafts, and a gearshift operation is performed by changing a gear engagement state thereof.
Patent Document 1: Japanese Patent No. 5143055
As an example of such techniques, Patent Document 1 discloses a multistage transmission in which a plurality of driving gears and a plurality of driven gears are supported about respective gear shafts parallel to each other while they mesh with each other in each gearshift stage at all times. In the technique discussed in Patent Document 1, a gear shift-up operation is performed by engaging a driven transmission gear having a gear reduction ratio smaller by one stage with a shaking pawl member R while the driven transmission gear n is engaged with the shaking pawl member R. Therefore, it is possible to achieve a smooth gearshift operation without a necessity of applying a force in disengagement and without using a gearshift clutch. In addition, there is no loss in a switching time for the shift-up operation. Furthermore, there is no loss of the drive force and little gearshift shock. Therefore, it is possible to achieve a smooth shift-up operation.
However, in the technique discussed in Patent Document 1, an internal structure of the counter gear shaft becomes complicated, and this increases a weight of the transmission mechanism and makes difficult to obtain a compact transmission mechanism.